Facts about White Melilot

Plant Description

White melilot is an annual or biennial, nitrogen-fixing herbaceous plant that normally grows about 2.5 m (8 ft. 2 in) in height. It is monocarpic which means that it dies after it flowers and sets seed. The first year, the plant grows a primary stem up to 1.5 m tall, and puts down a deep taproot. In ideal conditions it may flower and set seed in its first year. If the flowering is done in the second year, the plant will over-winter just under the soil surface and the stem will appear in spring. Roots don’t grow as much in the second year; most of the growth is done by the stem and energy is used to flower and set seed. White Sweet Clover is able to self-pollinate, meaning that a single plant can produce a new population.

The plant thrives in riparian habitats, grassland, pastures, disturbed places, fields and waste places, savannahs, sand dune, prairie, meadow habitats, roadside edges, railway rights-of-way, limestone glades, thinly wooded bluffs, agronomic fields, ditches, vacant lots and in hydro corridors. The plant grows best on deep, fertile, well drained, medium to heavy textured soils, but adapted to a wide range of calcareous, alkaline and saline soils. It grows naturally on a wide range of soil types and textures from clays to dune sand and river gravels and does not tolerate highly acidic soils.

Roots

White Sweet Clover or White melilot forms a taproot which can grow up to 1.5 m deep in the soil. Adventitious roots form on its stem and extend outwards 30-40 cm. Roots contract to pull the plant crown down slightly under the soil in the fall to help it survive winter and grow again in its second year.

Stems

The stem of White Sweet Clover is smooth and hairless, erect, ascending and branched, grooved or channeled. The stems are usually up to 1.5 m in height. The root crown produces somewhere between 1 to 10 stems.

Leaves

The leaves of White Sweet Clover have 3 leaflets, and are alternate along the stem. Leaflets of lower leaves are broadly ovate, obovate or rhomboidal, rounded or truncate at the tip, irregularly dentate, 7–35 mm long and 2–15 mm wide. Upper leaflets are narrowly oblong to lanceolate, usually rounded or truncate at the tip, dentate to almost entire. Each leaflet is fully toothed.

Flowers

White sweet clover flowers are very fragrant, with a vanilla-like scent. Flowers are arranged in spike clusters at the top of the plant. Individual flowers are white, roughly ¼ inches (0.6 cm) across. Flower spikes are around 8 inches tall and the flower stalks each have between 20 and 65 flowers. Each flower has 5 petals and a light green calyx with 5 teeth. The flower is tubular and becomes broader toward the outer edges of the petals. The flowers are similar in shape to pea flowers (both plants are legumes), but much smaller. Flowering normally takes place in between July to August.

Fruit & Seeds

Fertile flowers are followed by ovoid seedpods that are black to dark grey, smooth or slightly reticulated and about 0.3 inches long (3-4mm). Each pod usually contains one, but sometimes two seeds. The seeds are 2.5 mm long and 1.5 mm broad, yellow and oval to kidney shaped and each plant can produce up to 350,000 seeds. Average weight for 1000 seeds is 2.3 g. Seeds often remain on the plant over the winter and fall as it dries out.

Traditional uses and benefits of White Melilot

• The whole herb, harvested when in flower, is aromatic, carminative and emollient.
• It was at one time widely esteemed as a medicinal herb, though it has fallen from favor in recent times.
• The dried leaves consists of coumarin, this can be used as an anticlotting agent for the blood.
• The dried flowering plant has been used in ointments for external ulcers.
• It is a mild astringent used for typical uses like washes for wounds, inflamed eyes, etc.

Culinary Uses

• Leaves and seedpods are cooked as a bean soup.
• The pea-like seeds are used as a seasoning for bean and split-pea soups.
• Young shoots can be consumed raw or cooked.
• It can be added to salads or used as a potherb.
• Only fresh shoots should be used, the dried leaves contain coumarin.
• Flowers can also be consumed raw or cooked.
• The dried leaves are said to be used as a vanilla flavoring.
• Young leaves have been used for tea, cooked greens, salads, and flavoring.
• Flowers can be pan roasted in order to make granola.
• Young leaves can be eaten raw or cooked preferably before the plant blossoms.
• They are bitter and aromatic, usually used as flavoring in salads.
• Young shoots can be cooked and used like asparagus.
• The whole plant thoroughly dried can be used to make a tea with a hint of vanilla.

Other Facts

• Oil obtained from the seed is used in paints, varnishes etc.
• It has long been valued for its potential as a fodder crop, for soil and land reclamation, for stabilizing soil and roadside cuttings and for honey production.
• The dried leaves smell of new-mown hay and are used as an insect repellent.
• Dried leaves contain a substance called coumarin, this is an anti-clotting agent and has been used as a basis of the rat killer ‘warfarin’.
• The plant is a good green manure crop.
• It can be sown in the autumn and overwintered or sown from spring to mid-summer.
• It can be cut several times for compost material before being finally incorporated into the soil.
• Fast growing, it produces a high bulk of organic material and also fixes a large quantity of atmospheric nitrogen.
• It can also be grown under soft and top fruit, when it will expel mice.
• Its pleasantly-scented dried leaves have been used to scent linens and sleeping quarters.
• White and yellow sweet clover is considered valuable honey plants, and the foliage and seeds are consumed by wildlife.
• They are frequently cultivated for livestock forage and as a cover crop.
• Melilotus albus has been promoted in Australia for use on dry land soils affected by salinity.
• It has been used in herbal medicine. It includes dicoumarol, which is an anticoagulant. It also has high sugar content.
• White Sweet Clover is a threat to endangered grassland and prairie habitats in Ontario.
• It is allelopathic, meaning the roots release chemicals into the soil which can prevent the growth of native plants.
• Each individual plant can produce up to 350,000 seeds.
• Seeds can remain viable in the soil for up to 80 years.
• Seeds of this plant can be dispersed intentionally (in seed mix or rarely, as a cover crop) or unintentionally by vehicle tires, moving water, or as a contaminant in crop seed.

Precautions

• Dried leaves can be toxic though the fresh leaves are quite safe.
• Taken internally it can prevent the blood from clotting.
• Regular consumption of the plant might have detrimental effects on the liver.
• It can cause bloating in some people as well.

Different Control Measures

Control measures must be continued for a minimum of five years to ensure that seedlings/the seed bank is depleted. Monitoring must continue as seeds may sprout seedlings for up to 80 years. Many of these control measures, if done only once, will actually increase densities by stimulating re-growth.

Manual

Control Mowing/Cutting

Pulling can be effective in small areas in sandy soil, where the plants are in their first year and in the spring before they have developed a deep root system. Plants that haven’t yet flowered can be pulled and left on site as they will not produce seeds.

Pulling

Mowing or cutting the second year plants back to about 2.5 cm from the ground will reduce seed production and plant density. It will not eradicate the plants immediately and they may re-sprout in the 3rd year to produce seeds.

Digging

For fewer plants or new infestations, first year plants can be removed by digging them out of the ground. It is crucial to cut the root under the soil and to conduct follow up monitoring for any re-sprouts.

Grazing

Concentrated grazing during late summer and fall can reduce the root reserves of the plants, which may lead to plant mortality the next spring. However, grazing should be done with caution due to the concentration of coumarin (a chemical compound that causes blood thinning) in the plants. Cut plants should not be used as feed due to increased coumarin levels as the plant decomposes

Cultural Control

Burning

Extreme caution is necessary when using early season prescribed burning in prairies and oak savannahs. Seeds of White Sweet Clover are stimulated by fire, and will germinate rapidly following burns. Within a week the ground may be covered in White Sweet Clover seedlings. Fire may produce dense stands of White Sweet Clover where none existed prior to the burn. Several small test burns should be done before any large scale prescribed burn. This will show if there are White Sweet Clover seeds in the seed bank and if a prescribed burn will make the invasion larger. Large infestations of new White Sweet Clover seedlings resulting from prescribed burns are best dealt with by spraying with herbicide a week after the burn, when maximum germination of seed has occurred, but before other species are in actively growing again.

Shading

White Sweet Clover does not move into or establish in shade, so if restoration is being done where a native tree canopy is being reestablished, the shade provided by those species may out-compete White Sweet Clover.

Chemical Control

Chemical control for White Sweet Clover is usually not necessary unless it is a very large population that cannot be controlled using manual/mechanical means. If confronted with a large infestation chemical control may be used as described below

Herbicide Application

 Herbicides must be applied in accordance with all label directions. For an up-to-date list of herbicides labelled for White Sweet Clover control, visit the Pest Management Regulatory Agency’s web site at www.pmra-arla.gc.ca. The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)’s Publication 75, Guide to Weed Control is an excellent reference for all aspects of weed control, and includes a section on invasive plant management.

Foliar Spray

Refer to the label of the herbicide you are using for rates and instructions for foliar application. Anyone using a pesticide is responsible for complying with all federal and provincial legislation. Most non-domestic (i.e. commercial, restricted etc.) herbicides can only be applied by licensed exterminators

Legislation governing pesticide use

The Ontario Pesticides Act and Ontario Regulation 63/09 provide natural resources, forestry and agricultural exceptions which may allow chemical control of invasive plants on your property. Other exceptions under the Act include golf courses, and for the promotion of public health and safety.

Biological Control

Biological control is the use of an herbivore, predator, disease or other natural enemy to reduce established invasive species populations. Most invasive species have no natural enemies in their new habitats. Biological control aims to re-establish an ecological balance by selecting highly host-specific natural enemies from the country of origin, and moving them to the country where the invasive species is a problem. This is only done after extensive host-range testing in the country of origin or quarantine, to ensure that the potential bio-control agent is host-specific to the targeted invasive species. This method has been used successfully for invasive plants in North America, including Purple Loosestrife, Leafy Spurge, Diffuse Knapweed and St John’s Wort. There are many species which will feed on White Sweet Clover, including an alien sweet-clover weevil which is present in North America. However, no biological controls are currently being researched because of its use as a forage species in the US and in soil remediation and other industries.

References:

https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=516979#null

http://www.hear.org/pier/species/melilotus_albus.htm

https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomydetail?id=23989

https://pfaf.org/User/Plant.aspx?LatinName=Melilotus+albus

https://www.cabi.org/isc/datasheet/33693

https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:156656-2

https://en.wikipedia.org/wiki/Melilotus_albus

http://www.seasonalwildflowers.com/white-melilot.html

http://www.iucngisd.org/gisd/species.php?sc=1170

http://www.theplantlist.org/tpl1.1/record/ild-7888

https://indiabiodiversity.org/species/show/245347

https://gd.eppo.int/taxon/MEUAL

http://temperate.theferns.info/plant/Melilotus+albus

http://www.flowersofindia.net/catalog/slides/White%20Sweet%20Clover.html

https://plants.usda.gov/home/plantProfile?symbol=MEOF

http://www.minnesotaseasons.com/Plants/white_sweet_clover.html

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